This follow-up trial for those subjects in a randomized, double-blind, phase 2/3 trial of monotherapy vs. combination therapy with nucleoside analogues in HIV-infected persons with CD4 cells <=200 or >=500 mm3 provides the opportunity to carefully characterize subjects who have a well-defined nucleoside analog exposure history with respect to their symptomatic state, their CD4 trajectory, and their virologic profile, and to relate this to the response to new antiretroviral interventions.